1. Field of the Invention
The invention relates to a method for forming a transparent conductive film, more particularly to a method for forming a flexible transparent conductive film.
2. Description of the Related Art
Indium tin oxide (ITO) transparent conductive films have been widely adopted in flat panel displays or optoelectronic devices due to their intrinsic properties of high conductivity and good light transmittance. However, skilled artisans in the related field are still making lots of efforts to seek replacements for the ITO films because of their relatively high costs and poor mechanical properties.
Hui Wu et al. disclosed a method for making a conventional flexible transparent conductive film, which includes the following steps of: electrospinning polyvinyl acetate which contains copper acetate, so as to form on a glass substrate a plurality of electrospun polymeric fibers which constitute a web structure, which contain Cu precursors, and which have a diameter of 200 nm and a length of 1 cm; heating the web structure at 500° C. in air for 2 hours to transform the Cu precursor-containing web structure into a CuO nano-web structure (dark-brown color) and to remove the electrospun polymeric fibers; and annealing the CuO nano-web structure for 1 hour, thereby reducing CuO of the CuO nano-web structure into Cu so as to obtain the conventional flexible transparent conductive film of Cu nano-web structure (see “Electrospun Metal Nanofiber Webs As High-Performance Transparent Electrodes,” Nano Lett. 2010, 10, 4242-4248, abbreviated as Prior art 1).
Although the conventional flexible transparent conductive film made by the method of Prior art 1 can have a light transmittance of 90% and a sheet resistance of 50Ω/□, the step of annealing at high temperature (300° C.) is needed to reduce the CuO. Moreover, due to the intrinsic chemical activity of copper, when thermal oxidation or chemical corrosion occurs, the sheet resistance of the conventional flexible transparent conductive film may increase, resulting in relatively low durability and reliability.
Hui Wu et al. further disclosed a method for forming another conventional flexible transparent conductive film, which includes the following steps of: electrospinning a polymer-containing solution to form on a copper frame a polymeric network template, wherein the polymer-containing solution is, e.g., 10 wt % of a polyvinyl alcohol (PVA) aqueous solution or 14 wt % of a polyvinyl pyrrolidone (PVP) aqueous solution; depositing a conductive layer on one side of the polymeric network template via thermal evaporation under a base pressure of 10−6 Torr when Cr, Au, Cu, Ag, or Al is selected, via e-beam evaporation under a base pressure of 10−6 Torr when Pt or Ni is selected, or via magnetron sputtering under a working pressure of 5 mTorr when silicon or Indium tin oxide is selected; and transferring the polymeric network template onto a solid substrate, followed by dissolving the polymeric network template to form the conventional flexible transparent conductive film (see “A transparent electrode based on a metal nanotrough network”, Nature Nanotechnology, volume 8, June, 2013, 421-425, abbreviated as Prior art 2).
Although the conventional flexible transparent conductive film made by the method of Prior art 2 exhibits relatively high fatigue resistivity in comparison to ITO transparent conductive films, the step of depositing the conductive layer under vacuum is still needed and thereby significantly increases the production cost.